1. Field of the Invention
The present invention relates to an information recording medium and a process for reproducing the information therefrom, and more particularly to an information recording medium provided with a format capable of increasing the amount of information by reducing redundancy and capable of an improvement in the speed of access or reproduction, and a process for reproducing information from said medium for example in optical manner.
2. Related Background Art
In recent years reproduction of information utilizing optical information recording medium, such as an optical file or a compact disk, has become popular. More recently attention is being paid to the reproduction of information utilizing a card-shaped optical information recording medium, hereinafter called optical card, of superior portability and of a relatively large memory capacity.
FIG. 1 is a schematic plan view of an example of the recording format of an optical card.
An optical card 1 is provided with a recording area 2 in which plural bands 3 are arranged. In each band 3 there are arranged plural information tracks 4 each having a memory capacity of several ten to hundred bits. Each band is defined by reference lines 5. An arrow A indicates the moving direction of the optical card 1 in the information reproduction, while an arrow C indicates the scanning direction of an optical head for information reading at the reproduction of information.
FIG. 2 is a schematic view of an apparatus for reproducing the information from an optical card with the above-explained recording format.
The optical card 1 is reciprocated in a direction A by a rotary mechanism 6. The information recorded on the optical card 1 is read and reproduced, track by track, by an optical head 11. Light from a light source 7, such as a light-emitting diode, is concentrated by a lens system 8 and illuminates the optical card 1. The image of a track of said optical card 1 is imaged, by an imaging optical system 9, onto a linear sensor array 10. The image of the information track on the sensor array 10 varies with the movement of the optical card 1 in the direction A. The sensor array 10 scans several times while each information track is imaged on said sensor array. After the information of certain information tracks of a band is reproduced in this manner, the optical head 11 suitably moves in the direction C to image an information track of another desired band onto the sensor array and the recorded information is reproduced in the same manner.
FIG. 3 is a partial enlarged schematic view of the recording format of the optical card 1 shown in FIG. 1. In FIG. 3 a hatched area indicates signals "1" while a blank area indicates signals "0".
FIG. 3 illustrates an end portion of the recording area, in the direction A, of the optical card 1. In an information track area 201, an array of information bits in the direction C constitutes an information track. A reference line 202 and said information track area 201 constitute a band 203. The information track is composed of a group of unit data areas 204, each having 5 bits. The reference line 202 has a length of 6 bits in the direction C, of which two end bits are "0" while central four bits are "1" of a stripe shape with a narrower width than a bit length in the direction A, and each stripe is positioned corresponding to each information track.
The information reading from an information track with the sensor array 10 is initiated upon detection of the information "011110" of the reference line 202 signifying a proper alignment of the optical head with the information track. Then, with the movement of the optical card 1 in the direction A with respect to the optical head 11, the information "011110" of the reference line is erased and replaced by "000000". Thereafter, upon reception of the information "011110" again signifying another information track, a reading operation is conducted in the similar manner. In this manner the reference line 202 not only functions to separate and identify the tracks neighboring in the direction C, but also performs the same function for the tracks neighboring in the direction A.
For reproducing information over plural bands of an optical card of the above-explained format, the information tracks of each band are scanned by the movement of the optical head 11 in the direction C. In such operation, the position of the optical head 11 has to be controlled in such a manner that the image of the information track falls in the effective reading range of the sensor array 10 over the entire desired band 203. Said head position control can be achieved by positioning the reference line 202 of a desired band in a predetermined range of the sensor array 10.
On the other hand, for making access to a desired track on the optical card 1, the optical card 11 is moved in the direction C from a home position HP, and a band 3 to which the desired track belongs is selected by counting the number of the reference lines read by the optical head 11. Subsequently a track number area of the information track area 201 imaged on the sensor array 10 is reproduced by the movement of the optical card 1 in the direction A, and, upon detection of a track number of the desired track, the information of the data area of said track is reproduced.
Naturally the data recording area of such optical card should be as large as possible.
However, with the increase of the number of information tracks contained in a band, the number of bits of the track number area for track identification has to be increased, and such increase results in a decrease in the number of bits available in the data area and in a higher redundancy.
Besides the reproducing speed of such optical card should be as high as possible. Particularly in case the recorded information is image or acoustic information, a high reproducing speed is desirable since the minimum unit amount of such information often requires plural information tracks.
However, the above-mentioned increase in the number of bits in the track number area results in a decrease in the number of bits of the data area 204, thereby giving rise to an increase in the number of tracks required for recording the minimum unit amount of information and to a reduced speed of information reproduction.
Also as explained above, the reproducing speed of such optical card should be as high as possible, and such higher reproducing speed requires an efficient access to a desired track or band with the optical head.